Pressure ratio computer



E. A. BAUER PRESSURE RATIO COMPUTER wv mm Filed Nov. 28, 1960 INVENTOR. ERNEST A. BAUER BY l ATTORNEYS July 31, 1962 3,4o,790 PRESSURE RATi CMPUTER Ernest A. Bauer, Burbank, Caif., assigner to The Marquardt Corporation, Van Nuys, Calii., a corporation of California Filed Nov. 2S, 1961i, Ser. No. 72,622 11 Claims. Ci. 73-4i37) This invention relates to a static pressure ratio computer and more particularly, to a ratio computer for high temperature applications in which the values or" the pressures of the ratio are provided by static rather than by owing uid.

At the present time, it is common to utilize pressure ratios to obtain information concerning various conditions o jet engine operation, such as iiight Mach number and thrust, and to measure various conditions such as specificA fuel ow land exit nozzle eilciency. A measure of flight Mach number may be obtained from the ratio between static pressure and total pressure of the free stream air. Generally, present instruments utilized to compute this ratio depend upon air ow measurements for accuracy and all air flow methods for computation depend upon either mass continuity in an isothermal region or in temperature corrected pressure readings based on mass continuity in a non-isothermal region or they use bellows devices which are temperature limited in operation. With the extreme temperatures now encountered by high speed engines, flowing air used in the controls will dier in temperature from the air swallowed by the probes. Since the control measurements are performed in non-isothermal region, temperature compensations would be required if the mass continuity concept of measurement were utilized.

The present invention permits the computation of pressure ratios which are obtained from iiuids which enter static probes at very high temperatures. ln static lines, there is no flow during steady state so that pressures are the same throughout the lines, either with or without cooling. Cooling reduces the thermal activity of the molecules and increases the density of the uid in a proportionate manner so that the pressures at the cool end and the hot end of the lines remain the same. Also, static lines may be cooled without penalties of accuracy since Pitot tubes convert flow pressure to static pressure and the lines connected with the Pitot tubes at the measuring stations can be cooled past the point whereby ow is brought to a stop, with no decrease in measuring accuracy.

The computer of the present invention, when used to measure Mach number, has Pitot tube means which obtains the static pressure and total pressure of the air stream. These pressures `are both utilized in static pressure line so that the iluid at these pressures does not flow through the instrument.` A source of work medium, such as cool air, is utilized in the portions of the instrument which employ owing uid in pressure dividers, such as disclosed in U.S. Patent Re. 24,410 issued December 3l, 1957, to lohn A. Drake. The static pressure lines can,

of course, be cooled since such cooling would not interfere with the measuring accuracy, but since no flow exists in these lines, very high temperatures can be withstood.

It is, therefore, an object of the present invention to provide a static pressure ratio computer which utilizes static, rather than flowing iluid as sources of reference pressure.

Another object of the present invention is to provide a high temperature, ratio computer in which Pitot tubes are utilized to obtain static pressures representing static and total pressure in the air stream so that the computer measures flight Mach number.

These and other objects of the invention not specitically set forth above will become readily apparent from the accompanying descniption `and drawing which diagrammatioally illustrates the computer of the present invention.

A source of air at supply pressure Ps can be obtained for the instrument of the present invention by ambient air probe 1u carried by a jet engine (not shown). At high speeds, the air captured by probe 10 has too high a temperature for the air to be utilized in air ow measurements involving air ow past valves and through orices, both of which are subject to destruction at the high air temperatures. A passage 11 connects the probe with a heat exchanger 12 containing a plurality of cooling coils (not shown) receiving a cooling medium from passage 13 and discharging same through passage 14. The cold air at Working iluid pressure Ps leaves the heat exchanger through header 15 'which has branches 16, 17, 18 and 19 leading to the various components of the computer.

The branch 17 connects the pressure Ps with chamber 2li of a pressure-to-position transducer 21 through an inlet orice 22 having an area A22. The chamber 20 is divided into spaces Z3 and 24 :by a diaphragm 25 and the space 23, connected to branch 17, exhausts to pressure Pex through passage 26 containing outlet orifice 27 having an area A27. A passage 28 connects a iirst ratio pressure, such as tree stream static pressure P0 obtained from a free stream Pitot tube, with the space 24 where it is bal anced against the pressures PA in space 23 between the orices 22 and 27.

rl`he diaphragm 25 is connected with a valve stem 29 which extends through oriiice 27 and out through the side of passage 26. A needle valve 30 is secured to stem 29 and located at orifice 27 to vary the throat area thereof until equilibrium is reached between pressures Po and PA. The two orifices 22 and 27 and the space 23 form a pressure divider, such as described in U.S. Patent Re. 24,410 issued December 31, 1957, to John A. Drake. Due to the pressure divider geometry A22 PA* AMPS and for steady state operation AzzPSzPA and The branch 19 connects pressure PS with a chamber 32 of a pressure-to-position transducer 33 through an inlet orifice 34 having an area A34. The chamber 33 is divided into spaces 35 and 36 by a diaphragm 37 and the space 35 exhaust to pressure Pex through passage 38 containing outlet oriiice 39 having an area A39. A passage 4Q conects a second pressure of the ratio, such as free stream total pressure PTO' obtained from a free stream Pitot tube, with the space 36 where it is balanced against the pressure PB in space 35 between the oritices 3'4 `and 39.

The diaphragm 37 is connected with a valve stem 41 which extends through orice 39 and out through the side of passage 38. A needle valve 42 is secured to stem 41 and is located at oriiice 39 to vary the throat area thereof until equilibrium is reached between pressures PB and 3 Y Y PTO'. The two orifices 34 and 39 and space 3S vform a second pressure divider vin which A34 t PAQPS and for steady state operation Where PB=PTO The branch conduit 18 connects pressure PS with a third pressure divider 45 which comprises a passage 46 containing an inlet orifice 47 of throat Varea A47 and an outlet orifice 4S of throat area A48. The orilce 43 exhauststo pressure Pex land the space 49 between the oriccs containing control pressure Pc is connected by passage 50 with space 51 in chamber 52 also at pressure Pc, A needle valve 53 is positioned by stem 29 within the inlet Orice 47 and a needle valve 54 is positioned by stem '41 within the outlet Vorilice 48. VThe control pressure lc in spaces 49 and 51 is as follows:

Also, the orifices are so dimensioned that A4i=k11f27 for all positions XA of the stem 29, and

Y fls=k2 4as for all positions XB of the stem 41.

Thus, it can be shown from the above that QI P c=P s P T' b n Po 92 A34 Y The space 51 in chamber 52 is isolated from space 55 containing pressure PD by audiaphragm 56 to which is or'dividing out PS from the last two equations n=PTJ aAa Aso P 1621434 Since Y i PTOI t P0 lis a function of Machnumber, Y

i kiAaz kzss y' is vaYV constant-(the areas being constant), and

Y AQ() t j a.Y function of position XD of'fstem 57 (area A55 being 0 constant); it follows that Y r XD-nMi fwheiejMis Mach number. Obviously, the transducer 62 Yingmovement proportional to said second pressurefsaid Y diaphragm receiving said second static pressure-onV oneY Y side, a pressure divider having two orilces in series iconcan produce a voltage or other physical signal propor-Y tional to XD and therefore to Mach number.

The present invention is insensitive to changes in working iluidY pressure or temperature. While the line supplying the working fluid at pressure PS can containa cooling unit 12, such a unit is unnecessary if a source of working uid is available at a temperature which can be withstood by the various orifices and valves subject to the ilowing medium. Further, the static lines 2S and 49 supplying the pressures PO and PTO may 'be cooled any 4desired amount by heat exchangers 63 and 64 lwithout changing the static pressures in the spaces 24Y and 36, respectively, rom the Pitot pressure. In other words, the static pressures in the static lines remain constant regardless of fluid temperature changes inthe lines. Since, in the present device, the fluids at the static pressures do not flow, the temperature of the fluid at these! pressures can be very high before requiring cooling in the static pressure lines. Y Y Y i Because the pressure PS of the working iluid is the same in all the pressure dividers, the shifts associated with altitude eiects due to Reynolds number changesfare cancelled out. The exhaustpressure can lbe, any suitable low pressure sink and the pressure difference lbetween the supply pressure Ps Vandthe exhaust pressure Pex is'genl erally sucient to .chokeY the orifices of all Vthe pressure dividers so that sonic flow exists at the orifice throats. Since the invention produces an output proportional to a pressure ratio, it can equally well Ibe utilized to compute pressure recovery, thrust or specic fuel ow in an engine Iby changing Ithe parameters monitored by lthe e static pressure probes. While the invention has been described in connection with a pressure ratio computer, it is apparent that the pressure-to-position transducers 2,1 and 33 utilize the invention since static pressure rather than the pressure of a owing fluid is utilized in Vone chamber and the flowing iiuid in the other chamber may be cooled. Various other modifications are contemplated by those skilled in the art without departing from the spirit and scope of the Iinvention as hereinafter definedV by the appended claims. Y What is claimed is: 1

1.Y AY pressure ratio computer comprising iirst means for producing aY movement proportional to a first static pressure of said ratio, second means for producing a movemeut proportional to a second static pressure of said ratio, third means responsive to both said movements for dev riving from a Working iluid pressure a control pressure Pc proportional to the pressure ratio and to the Working Y Aa pressure divider having two orices in series connectedV with said working fluid pressure, the pressure intermediate the orices of said pressure divider being connected with the other side of `said diaphragm, the area of one of said orifices being controlled by phragm.` t

3. A pressure ratioY computer. as defined Ain claim 1 wherein said. second means comprises ar diaphragm havthe movement ofrsaiddianected with said working uid pressure, the pressure intermediate the orices of ysaid pressure divider being connected with the other side of said diaphragm, .the area of one of said orifices being controlled bythe movement ofsaid diaphragm,

4. A pressure ratio computer-.as defined in claim lf wherein said third means comprises a pressure divider having a pair of spaced orices connected with `said working fluid pressure, a first needle valve connected with said rst means for varying the area of one orice, and a second needle fvalve connected with said second meanS for varying the area of the other orifice, said control pressure existing in the space between said oriiices.

5. A pressure ratio computer as defined in claim 1 wherein said fourth means comprises a diaphragm receiving said control pressure on one side thereof, a pressure divider having a pair of spaced orifices connected with said working fluid pressure, and means connected with said diaphragm for varying the area of one of said orices, the movement of said varying means providing the output movement proportional to said pressure ratio.

6. A pressure ratio computer comprising first diaphragm means in a first static chamber and receiving a first static pressure of said ratio on one side thereof, means responsive to the movement cf said first diaphragm means for producing a balancing pressure on said irst diaphragm means opposing said first pressure, second diaphragm means in a second static chamber and recovering a second static pressure of said ratio on one side thereof, means responsive to the movement of said second diaphragm means for producing a balancing pressure on said second diaphragm means opposing said second pressure, a pressure divider having the area of one orifice controlled by said rst diaphragm means and the area of the other orifice controlled by said second diaphragm means to produce a control pressure lc between the orifices proportional to the pressure ratio and to the supply pressure PSX for the pressure divider, third diaphragm means receiving said control pressure on one side thereof, a second pressure divider receiving said supply pressure and responsive to movement of said third diaphragm means for producing a balancing pressure on said third diaphragm means opposing said control pressure, and means positioned by said third diaphragm means for providing a measure of said pressure ratio.

7. A pressure ratio computer as defined in claim 6 wherein each of said balancing pressure producing means comprises a pressure divider connected with said supply pressure and having an orifice variable in area by one of said diaphragm means.

8. A pressure ratio computer as defined in claim 7 wherein said supply pressure is derived lfrom a source of high temperature gas, and means for cooling said gas before entering all said pressure dividers in order to prevent damage to said pressure dividers by the flowing high temperature gas.

9. A pressure ratio computer as defined in claim 6 wherein said first static pressure is derived from a static supply line receiving high temperature gas, and means for cooling the gas in said supply line without changing the static pressure in said first chamber.

10. A pressure ratio computer as deiined in claim6 wherein said second static pressure is derived from a static supply line receiving high temperature gas, and means for cooling the gas in said supply line without changing static pressure in said second chamber.

ll. A pressure ratio computer comprising a first static chamber receiving a first pressure of the ratio, a second static chamber receiving a second pressure of the ratio, a source of working fluid supplied to first and second pressure dividers, each comprising rst and second spaced orifices, a first diaphragm separating the space between the orifices of the irst pressure divider from said first pressure, a second diaphragm dividing the space between the oriiices of said second pressure divider from the space con- -taining said second pressure, a valve stem connected to said first diaphragm and carrying a needle valve for controlling the throat area of one ofthe orifices of said first pressure divider to produce a pressure between the first divider orices equal to the first pressure, a second valve stem connected to said second diaphragm and carrying a needle valve for controlling the throat area of one of the orifices of said second pressure divider to produce a pressure between the second divider orices equal to the second pressure, a third pressure divider receiving said working fluid and comprising spaced orifices, a needle valve carried by said first stem for controlling one of said third divider orifices and `a needle valve carried by said second stem for controlling the other of said third divider orifices, the space between the orifices of said `third pressure *divider being connected with one side of-a third diaphragm, a fourth pressure divider receiving said working medium and having spaced orifices, and a third stem connected to said third diaphragm for controlling the area of one of the orifices of said fourth pressure divider to balance the pressures on said third diaphragm, .the position of said fourth stem being an indication of said pressure ratio.

References Cited in the file of this patent UNITED STATES PATENTS 2,981,058 Reed Apr. 25, 1961 2,986,929 Reed i June 6, 1961 FoRErGN PATENTS 59,596 Netherlands June V17, 1947 

